System for controlling liquid level



July 1, 1958 P. L. WALKER ll SYSTEM FOR CONTROLLING LIQUID LEVEL FiledJuly 28, 1954 INVEA/TQR. PRESTO/V L. WALKER H his Alia/nay.

Uni d ta es Patent SYSTEM FOR CONTROLLING noun) LEVEL Preston L. WalkerII, Birmingham, Ala., assignor to United States Steel Corporation, acorporation of New Jersey Application July 28, 1954, Serial No. 446,233

22 Claims. (Cl. 118- -7) This invention is directed to an improvedsystem for controlling the level of liquid material in a reservoir orreceptacle and, more particularly, to a system for maintaining the levelin a reservoir from which material is withdrawn gradually and constantlyby working operations and to which make-up or replacement material isadded periodically in large batches, the rate of material replacementbeing relatively-high compared to its rate of withdrawal.

More specifically, the liquid level system of this invention isparticularly adapted to maintenance of the surface level of a moltenmetal bath in metal coating operations in which a strip of steel ispassed through the bath of coating metal and to which make-up metal isadded in the form of pigs.

In galvanizing and other metal coating operations, steel strip is passedthrough a bath of molten coating metal to apply a covering of thecoating metal thereto; Since the surface level of the bath afiects thethickness of the coating on the strip, it is desirable to maintain thesurface of the bath at a constant level. In conventional practice, thisis accomplished manually under the control of an operator who adds pigsto the bath as needed and its surface level thus varies over wide limitsdepending upon the skill of the operator. The maintenance of the surfacelevel of a coating metal bath is further complicated by reason of thefact that the movement of the strip through the bath Withdraws coatingmetal therefrom at a gradual and continuous rate while the addition of apig results in the make-up metal being supplied in a relatively largebatch or quantity in a much shorter period of time. The addition of apig in this manner thus causes an upward surge in the surface level ofthe coating metal bath which is determined by the size of the pig added.

One of the principal objects of this invention is to provide a liquidlevel control system for coating metal baths which does not depend onthe skill of an operator.

A further object of the invention is to provide a systern forcontrolling the surface level of fluid materialin a reservoir from whichit is withdrawn gradually by working operations and to which make-upmaterial is added in relatively large batches.

Another object of the invention is to provide a system of the characterjust referred to which feeds batches of make-up material in accordancewith the surface level requirements of the reservoir and which will tendto maintain such surface level within the limits determined by theaddition of a single batch.

Another object of the invention is to provide a level control system ofthe character referred to having a batch feeding mechanism which isrendered operative to feed a single batch of material in response tochanging conditions of the surface level and which has provisions forpreventing the addition of a subsequent batch until after the surfacelevel has responded to the batch previously added.

2,841,111 Patented-July 1, 1958 A still further object of the inventionis to provide a system for controlling the surface level of a moltenmetal coating bath in metal coating apparatus having a feed mechanismeffective upon each operation thereof for feeding a single predeterminedquantity or batch of coating metal to the bath in the form of pigs, andwhich includes means responsive to the surface level of the bath fallingto a predetermined minimum for rendering the pig feeding mechanismoperative, together with a timing mechanism for introducing apredetermined minimum time interval between each operation of the pigfeeding mechanism to enable the surface level responsive means torespond to changes in surface level resulting from a single pig feedingoperation of the feeding mechanism before it is permitted another suchoperation.

Other objects and advantages of the invention will become apparent fromthe following description.

In the drawings there is shown a preferred embodiment of the invention.In this showing:

Figure l is a diagrammatic illustration of a level control systemconstructed in accordance With the principles of this invention andapplied to a spelter pot in a galvanizing line; and

Figure 2 is a sectional view of a pressure differential regulator forcontrolling the flow of gas through the surface level responsivemechanism shown in Figure 1.

In the drawings, the numeral 1 designates a reservoir or receptaclecontaining a bath 2 of molten coating metal through which steel strip Sis passed to apply a covering of the coating metal thereto. The bath 2,for example, may be spelter and the receptacle 1 may be the spelter potin a conventional continuous galvanizing line. While the strip S isillustrated diagrammatically as being continuous, it will be understoodthat the principles of the invention as explained hereinafter areapplicable to single sheet coating operations, and to coating operationsusing coating metals other than zinc. Movement of the strip S throughthe bath 2 removes metal therefrom and results in a lowering of itssurface level 3.

- To replace metal removed from the bath 2 by the strip S, there isprovided a magazine 4 containing a stack of pigs 5. An air cylinder 6having a piston 7 therein operates an ejector 8 to deliver the lowermostpig in the magazine 4 to a conveyor chute 9 for delivery thereby to apro-melt pot 10. The pre-melt pot 10 has an overflow passage 11connecting it with the spelter pot 1 and has heating apparatus (notshown) for maintaining the body of metal 12 therein in molten conditionand for melting pigs 5 fed thereto. The spelter pot 1, similarly, and inaccordance with conventional practice, has heating apparatus (not shown)for maintaining the bath 2 at a proper temperature. When a pig 5 is fedto the premelt pot 10, the level of the metal 12 therein is raised and aquantity of molten metal equivalent to that in the pig 5 deliveredthereto overflows through the passage 11 into the main pot 1. In thismanner, the surface level 3 in the main pot 1 is elevated by theoverflowing metal delivered through the passage 11 upon each operationof the cylinder 6 to eject a pig from the magazine 4. The parts of theapparatus thus far described are conventional and form no part per se ofthis invention, this invention being directed to a system forcontrolling the delivery of pigs 5 to the pre-melt pot 10 and therebyfor controlling the level of the surface 3.

In accordance with the principles of this invention, the operation ofthe pig ejecting cylinder 6 is controlled in such manner that the levelof the surface 3 is maintained above a predetermined minimum. This isaccomplished, in a manner to be described by a surface level responsiveapparatus designated as" a whole by the letter L which produces acontrol pressure varying with the controller designated as a whole bythe letter P, and a control circuit designated as a whole by the letterC which controls the operation of a reversing valve R for the aircylinder 6.

The reversing valve R is of conventional construction and isdiagrammatically illustrated. It comprises a valve rod 14 mounted forendwise movement to either of two positions in a valve casing 15 forreversing the connections of the ends of the cylinders 6 throughconduits 16 and 17 with respect to an air supply connection 18. A spring19 biases the movement of the rod 14 to the right as viewed in .Figure 1to a position seating a pair of valve elements 20 mounted thereon andopening a similar pair of valve elements 21. In this position, theconduit 17 is connected with the air supply connection 18 through one ofthe open valve elements 21 and the conduit 16 is connected to theatmosphere through the other of the open valve elements 21 and anexhaust port connection 22 in the valve casing. A solenoid 23 isprovided for moving the valve rod 14 to the left against the action 'ofthe spring'19 to close the valve elements 21 and open the valve elements20 and thereby reverse the connections ofthe conduits 17 and 16 with theatmosphere and with the air supply passage 18. Movement of the valve rod14 by the solenoid 23 in this manner is effective to move the piston 7and plunger 8 to the right for delivering a pig 5 to the pre-melt pot10. When the solenoid 23 is de-energized, the spring 19 returns thevalve rod 14to the position illustrated, and the piston 7 and plunger 8are returned to the position shown in the drawings for effecting anotherpig ejecting operation.

Operation of the reversing valve R by the solenoid 23 is controlled bythe circuit C which in turn is actuated by the pressure responsiverecorder-controller P and the level responsive device L. The parts L andP are conventional structures which may be purchased on the market in aform suitable for the purposes of this invention. For example, thepressure responsive device L may be obtained from the Fischer & PorterCo. of Hatboro, Pennsylvania and is of a type illustrated in itscatalogue l0-A29 dated February 9, 1954. Similarly, the pressurerecorder-controller P may be obtained from The Bristol Company ofWaterbury, Connecticut and is of a type illustrated in its publicationentitled Bulletin F1605. Since this invention is not concerned with thespecific construction of the units L and P, they have been showndiagrammatically in the drawings for the purpose of illustrating themanner in which they operate the control circuit C.

The level responsive device L comprises a conduit 25 which delivers gasat a constant rate to a vertically extending dip tube 26 having anoutlet 24 at its lower end positioned below the surface 3 and throughwhich gas escapes or bubbles through the bath 2. Gas is delivered to theconduit 25 from a suitable source under pressure by a conduit 27 andthrough a pressure reducing valve 28, a constant pressure differentialvalve 29, and a throttle or needle valve 30, the valve being adjustableto control the quantity of gas being supplied to the dip tube 26. Thegas supplied to the tube 26 is a non-oxidizing gas, preferably NX gasalthough any other non-oxidizing gas may be used, which will not oxidizethe molten metal 2 through which it escapes. The valves 28, 29 and 30operate to deliver gas at a constant rate through the dip tube 26 andthe pressure of the gas in the conduit 25 thus provides an indication ofthe level of the surface 3 and which varies with changes in the distancebetween the surface 3 and the outlet 24.

The manner in which the pressure differential valve 29 maintains theflow of gas through the conduit 25 at a constant rate will be bestunderstood by referringto Figure 2. In this showing, a diaphragm 31 ispositioned between an upper pressure chamber 32 and a lower pressurechamber 33. The chamber 32'is connected by a conduit 34 with the conduit25 so that the pressure therein corresponds to the pressure of the gasin the conduit 25. The lower chamber 33 has an inlet 35 and an outlet 36connected in the conduit 27 so that the pressure therein corresponds tothe pressure in the conduit 27. The force of the pressure in the chamber33 acting against the diaphragm 31 is balanced by the pressure in thechamber 32 and the action of a biasing spring 37 which acts downwardlyagainst the diaphragm 31. A valve 38 having a spring 44 biasing itupwardly to a position engaged with the diaphragm 31 controls theeffective connection between the inlet 35 and the outlet 36. When thediaphragm 31 moves downwardly in response to increased pressure in thechamber 32, the valve 33 is moved downwardly to increase the effectivesize of the valve connection between the inlet 35 and outlet 36. In thismanner, the pressure of the gas moving through the outlet connection 36is increased to compensate for the increased pressure in the conduit 25so that the flow of gas through the conduit 25 will not be diminished.Increases of pressure in the conduit 25 and chamber 32 are caused by arising level of the molten metal bath surface 3. 'When the surface 3 ofthe molten metal bath falls, the pressure of the gas in the conduit 25and chamber 32 decreases and the diaphragm 31 moves upwardly to renderthe valve 38 effective to reduce the pressure of the gas delivered tothe outlet 36 while maintaining its rate of flow through the conduit 25constant. By maintaining the rate of flow of gas through the conduit 25constant, the pressure therein provides an indication of the verticalposition of the surface level 3.

A relief device 39 is provided for relieving the system of surgingpressures in the conduit 25 and for eliminating the effects of suchpressures on the differential valve 29. The relief device 39 comprises acontainer partially filled with a body of mercury 40 and having a port41 to the atmosphere. A tube 42 is connected with conduit 25 and has itslower end 43 immersed in the mercury 40. Surging pressures in theconduit 25 will thus be absorbed by the relief device 39 and will beeffective only to move the level of the mercury in the tube 42 upwardlyor downwardly depending upon whether the surge is an increase ordecrease.

Energization of the circuit C to operate the solenoid 23 is maderesponsive to the surface 3 falling to a predetermined level at whichthe pressure in the conduit 25 will be at a predetermined minimum. Thisis accomplished by a recorder-controller P which, as indicated above,has been shown diagrammatically for the purpose of illustrating themanner in which this action takes place. In the drawings, therecorder-controller P is shown as having a stationary contact 45 and amovable contact 46 connected to a rotatable pointer or indicator 47which moves relatively to a scale 48. The pointer 47 is operated by afloat 49 which moves vertically with the level of the body of mercury 50in a low pressure chamber 51 which is ported to the atmosphere by a tube52. A high pressure chamber 53 in the form of a sealed container has itsupper end connected by a conduit 54 with the conduit 25 and is partiallyfilled with a body of mercury 55. The lower end of the container 53 isconnected with the chamber 51 by a tube 56 so that the level of themercury 50 in the chamber 51 varies with the pressure in the upperportion 57 of the chamber 53, the pressure in the chamber 57 varyingwith the pressure in the conduit 25 and thereby with the level of thesurface 3 of themolten metal bath in the reservoir 1.

As the level of the surface 3 drops, the pressure in the chamber 57decreases thereby causing the level of the body of mercury 55 to riseand the level of the body of mercury 50 to fall. As the level of themercury 50 falls, the float 49 moves downwardly and pivots the pointer47 in a counter-clockwise direction. Pivotal movement of the pointer 47continues in this manner until the contact 46 carried thereby engagesthe contacts 45'. Engagement of the contacts 45 and 46 energizes thecircuit C in a manner to be described to render the cylinder 6 effectiveto deliver a pig 5 to the pre-melt pot to thereby raise the level of thesurface 3 of the bath 2 as explained above. Raising the level of thesurface 3 increases the pressure in the chamber 57 thereby reversing theflow of mercury through the tube 56 to raise the float 49 and pivot thepointer 47 to disengage the contacts 45 and 46.

The indicator 48 may be calibrated in terms of the position of thesurface 3 so that it provides a continuous indication of its level. Asin the commercial form of recorder-controller P obtained from theBristol Company as mentioned above, the pointer 47 may conveniently be arecording pen cooperating with a rotating chart for providing apermanent record of the level of the surface 3 at any given time. Inaddition, and as in the Bristol Company form of recorder-controller P,closure of the circuit C may be effected by causing move- In'ent of thepointer P to vary the impedance of an electri'c'al circuit coupled to anamplifier which in turn operates a relay, operation of the relay in suchcase corresponding to closure of the contacts 45 and 46.

-With reference to the control circuit C, operation of the'reversingvalve operating solenoid 23 is controlled by energization of a controlrelay 60 having a control relay switch 61 and a holding relay switch 62.An energizing circuit for the control relay 60 is completed acrossalternating current supply buses L1 L2 through a main circuit 63connected at the point 64 to the bus L2 and having a limit switch 65connected in series therewith, and through a pair of branch circuits 66and 67 connected respectively with the bus L1 at the points 68 and 69.The branch circuit 66 is connected with the circuit portion 63 uponclosure of the holding relay switch 62 and the branch circuit 67 issimilarly connected with the circuit portion 63 upon engagement of arotating contact 70 with a stationary contact 71 of arcuate shaperespectively in the branch circuit 67. The rotatable contact 70 isoperated by a synchronous motor 72 which is connected across the busesL1 and L2 by conductors 73 and 74 upon engagement of the contacts 45 and46.

In the operation of the circuit C, engagement of the contacts 45 and 46connects the motor 72 through the leads 73 and 74 to the supply buses L1and L2 so that it becomes effective to rotate the contact 70. When therotating contact 70 engages the contact 71, and it will be noted thatthe contacts 70 and 71 engage onlymomentarily because of the rotatingmovement of the contact 70 the branch circuit 67 will be energized and,since it is connected directly with the main circuit portion 63 at thepoint 75, an energizing circuit for the relay 60 will be completedthrough its operating coil 76 to the connection 64 with the supply busL2. Relay 60 will thus be energized to close relay contacts 61 and 62.Closure of relay contact 62 will be effective to establish a holdingcircuit through the branch circuit 66 for maintaining relay 60 operatedafter the rotating contact 70 moves beyond the stationary contact 71 andopens the branch energizing circuit 67.

Closure of relay contact 61 established an energizing circuit for theoperating coil 77 of the solenoid 23 which may be traced from theconnection 68 with the bus L1 through the branch circuit 66, relayswitch 61, coil 77, and the connection 78 with the bus L2. Energizationof the coil 77 in this manner operates the reversing valve R by movingthe valve stem 14 against the action of the biasing spring 19 to causethe piston 7 to move to the right as viewed above and deliver a pig 5 tothe pre-melt pot 10. As the piston 7 moves to the end of its pigejecting stroke, a lug 80 secured to its piston rod engages and movesthe limit switch 65 to open position against the action of a biasingspring 81 which is effective normally to hold it in a closed position.Opening of the limit switch 65interrupts the energizing circuit for thecoil 76, and the relay 60 drops out and switches 61 and 62 open. Openingof relay switch 61 de-enei'gizes the operating coil 77 for the solenoid23 and the reversing valve R is then operated by its biasing spring 19to reverse the connections of the cylinder 6 and return the piston andejector 8 to the position shown in the drawings.

It will be recalled that the contacts 70 and 71 engage momentarily andthat rotation of the contact 70 by the motor 72 is effective to move itout of engagement with the contact 71 after completion of the holdingcircuit 66 through the relay switch 61. Since opening of the limitswitch 65 causes the holding relay switch 61 to move to open position,it will-be apparent that a second operation of the solenoid 23 and anaddition of another pig 5 to the pre-melt pot 10 will not be haduntilthe contact 70 rotates to a position in which it again engages with thestationary contact 71, and this action will not take place until apredetermined time interval has elapsed after the first pig ejectingoperation of the cylinder 6. To provide the time interval for thispurpose, the motor 72 is a synchronous motor which is' connected withthe contact 70 through a speed reducing connection 83 which is effectiveto rotate the contact 70 at a speed of from about /2 to 1 R. P. M. Ifrotated at a speed of about 1 R. P. M., an interval of about 45 secondswill elapse between successive engagements of the contacts 70 and 71, ifrotated at a speed of about /2 R. P. M., an interval of about 1 /2minutes will elapse between successive engagements of the contact 70 and71. The timed intervals between the successive engagements of thecontacts 70 and 71 control the rate at which pigs are delivered to thepre-melt pot 10 and enable the apparatus L and P to respond to changinglevels of the surface 3 due to each addition of a pig 5. If theelevation of the surface 3 by the addition of a pig 5 is suflicient toopen the contacts 45 and 46, the motor 72 will stop and the delivery ofpigs to the pre-melt pot 10 will be discontinued until a' subsequentengagement of the contacts 45 and 46 in response to the level 3 fallingbelow a predetermined point. Under normal operating conditions, thecontacts 45 and 46 can be expected to open after the addition of asingle pig, and the operation of the apparatus will be effective tomaintain the surface 3 at a level which varies between upper and lowerlimits determined by themetal in a single pig.

The time delivery interval provided by the synchronous motor 72 andspeed reducing connection 83, and intermittently engaging contacts 7071may be conveniently effected by a timing mechanism produced by EagleSignal Corporation of Moline, Illinois as shown in its Bulletin 320 ofDecember 1950 wherein it is designated by the name Flexopulse repeatcycle timer.

A manually operable push button 85 is provided for transferringoperation of the apparatus from automatic to manual'control. Actuationof the switch 85 opens the connection of branch circuit 67 to theintermittently engaged contact 71 and renders effective a manuallyoperable energizing circuit 86. A push button switch 87 controlsenergization of thecircuit 86 and, when it is operated to closedposition, the main circuit 63 is energized through the circuit 86.Energization of the main circuit 63 will operate the reversing valve Ras described above, and a pig 5 will be delivered to the pre-melt pot 10on each operation of the push button switch 87 as long as the switch 85is in a position rendering the circuit 86 operative.

In the operation of the apparatus, coating of strip S gradually andcontinually withdraws coating metal from the bath 2. When its surface 3drops to a predetermined level, the decreasing pressure in the levelresponsive device L operates the recorder-controller P to close thecontacts 45-46. Closure of the contacts 45-46 energizes the circuit C toeffect a single working cycle of the reversing valve R and thereby todeliver a single pig to the reservoir of molten coating metal containedin 7 the pets .1 and 10. The deliveryof .a single pig will 'be effectivenormally to raise .the surface '3 above the predetermined minimum level,and the device L will operate through the recorder-controller P to openthe contacts 45-46 and dc-energize the circuit C. If the .addition of asingle pig is insufficient to raise the surface 3 above itspredetermined minimum level, the apparatus will continue to deliver pigsat timed intervals until the surface 3 rises above its predeterminedminimum level.

From the foregoing, it will be apparent that the apparatus of thisinvention is effective to replace the coating metal in the bath 2 inaccordance with withdrawals therefrom by the strip S, and that this isaccomplished without attention on the part of .an operator. Attention isparticularly directed to the fact that the apparatus goes ino operationwhenever the level of the surface 3 drops below a predetermined minimumand stops when the surface 3 is above the predetermined minimum. When itis considered that each batch or pig delivery results in the metal ineach pig delivery being distributed over. the relatively large area ofthe surface .3, it will be appreciated that the level of the surface 3is maintained within close limits. In this manner, and notwithstandingeach pig delivery results in an instantaneous addition of a relativelylarge batch of coating metal to the reservoir of molten coating metal,the apparatus operates to maintain the surface 3 at a level which issubstantially constant so that a coating of uniform thickness will beapplied to the strip S moving through the bath 2.

While one embodiment of my invention has been shown and described itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

I claim:

1. In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a single solid batch of materialto said reservoir to replace the material withdrawn, a control systemfor maintaining the level of material in said reservoir above apredetermined minimum comprising actuating means for operating said feeddevice, means controlling the operation of said actuating means, andmeans responsive to the level of material in said reservoir fallingbelow said predetermined minimum for operating said control means.

2. In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a single solid batch of materialto said reservoir to replace the material withdrawn, a control' systemfor maintaining the level of material in said reservoir above apredetermined minimum comprising actuating means for operating said feeddevice, means for producing a fluid pressure varying with the level ofmaterial in said reservoir, and means responsive to said fluid pressurefalling to a predetermined minimum value for operating said actuatingmeans.

3. In an apparatushaving a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a single solid batch of materialto said reservoir to replace the material withdrawn, a control systemfor maintaining the level of material in said reservoir above apredetermined minimum comprising actuating means for operating said feeddevice, a tube extending into said reservoir and having an outletpositioned below the surface level of the fluid material therein, meansfor forcing a gas at a constant rate through said outlet whereby thepressure of the gas in said tube at a point remote from said outletvaries with the surface level of said fluid material, and meansresponsive to said pressure falling to a predetermined minimum foroperating said actuating means.

4, In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof vto deliver a relatively large batch ofmaterial to said reservoir to replace the material withdrawn, a controlsystem for maintaining the level of material, in said reservoir above apredetermined minimum comprising actuating means for operating said feeddevice, means controlling the operation of said actuating means, andmeans responsive to the level of material in said reservoirfalling'below said predetermined minimum for rendering said controlmeans operative, said control means including means for eflectingintermittent operations, of said actuating means and for introducing atimed interval between each operation of said feed device therebysufficient for said level responsive means to respond to the change inlevel of material in said reservoir caused by the batch of materialadded by each operation of said feed device. a

5. In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a single solid batch of materialto saidreservoir to replace the material withdrawn, a control system formaintaining the level of material in said reservoir above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, a relay controlling the operation of said actuatingmechanism, means responsive to the level of material in said reservoirfalling below said predetermined minimum for operating said relay torender said actuating mechanism operative, and means responsive to thecompletion of a batch feeding operation of said feed device by saidactuating mechanism for operating said relay to render said actuatingmechanism inoperative.

6. An apparatus as defined in claim 5 characterized by said said levelresponsive means including means for rendering it inoperative to effectsubsequent operations of said relay for a predetermined period of timeafter the completion of each batch feeding operation of said feed deviceby said actuating mechanism.

7. In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a relatively large batch ofmaterial to said reservoir to replace the material withdrawn, a controlsystem for maintaining the level of material in said reservoir above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, an electrical relay controlling the operation of saidactuating mechanism and including an energizing circuit effective whenclosed to render said actuating mechanism operative and when opened torender said actuating mechanism inoperative, a normally closed limitswitch in said circuit, a control switch for closing said circuit, meansresponsive to the level of material in said reservoir falling below saidpredetermined minimum for operating said control switch to close saidcircuit, and means responsive to the completion of a batch feedingoperation by said device for momentarily actuating said switch to openposition to open said circuit.

8. In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a relatively large batch ofmaterial to said reservoir to replace the material withdrawn, a controlsystem for maintaining the level of material in said reservoir above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, an electrical relay controlling the operation of saidactuating mechanism and including an energizing circuit effective whenclosed to render said actuating mechanism operative and when opened torender said actuating mechanism inoperative, a normally closed limitswitch in said circuit, a control switch in said circuit movable betweenopen and closed positions, means for operating said control switchbetween its open and closed positions and for maintaining it in its openposition for a predetermined interval of time after each movement toclosed position, means responsive to the level of material in saidreservoir, falling below said predetermined minimum for operating saidcontrol switch operating means, and means responsive to the completionof a batch feeding operation by said device for momentarily actuatingsaid limit switch to open position to open said circuit. I

9. In an apparatus having a reservoir from which fluid material iswithdrawn gradually by working operations and a feed device effectiveupon each operation thereof to deliver a relatively large batch ofmaterial to said reservoir to replace the material withdrawn, a controlsystem for maintaining the level of material in said reservoir above apredetermined minimum comprising an actuating mechanism adapted eachtime it is rendered operative to effect a single batch deliveryoperation of said feed device, a control relay for rendering saidactuating mechanism operative, a control circuit for energizing saidcontrol relay and having a normally open first relay switch therein, anoperating relay, an operating circuit for energizing said operatingrelay and having a main circuit and a pair of branch energizing circuitsconnected therewith, a normally closed limit switch in said maincircuit, one of said branch energizing circuits having a normally opensecond relay switch therein and the other having a control switchtherein, means responsive to the level of material in said reservoirfalling below said predetermined minimum for operating said controlswitch to energize said operating circuit and said. operating relay,said oper-. ating relay having connections for closing both said firstand second relay switches upon energization thereof, and meansresponsive to the completion of a batch delivery operation of said feeddevice by said actuating mechanism for momentarily operating said limitswitch to open position to open said operating circuit and de-energizesaid operating relay to thereby de-energize said control circuit andcontrol relay.

10. An apparatus as claimed in claim 9 characterized by said levelresponsive means including means for operating said control switchperiodically and at timed intervals to closed position to therebyprovide a predetermined timed interval between each of the batchdelivery operations of said feed device required to raise the level ofmaterial in said reservoir at least to said predetermined minimum.

11. An apparatus as claimed in claim 9 characterized by said levelresponsive means comprising means for producing a fluid pressure varyingwith the level of material in said reservoir, an energizing circuithaving an operating switch therein, and means responsive to said fluidpressure for actuating said operating switch.

12. An apparatus as claimed in claim 11 characterized by said pressureproducing means comprising a tube eX- tending into said reservoir andhaving an outlet positioned below the surface level of the fluidmaterial therein, and means for forcing a gas at a constant rate throughsaid outlet whereby the pressure of the gas in said tube at a pointremote from said outlet varies with the surface level of said fluidmaterial.

13. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto,means for supplying pigs of coating metal to said bath to replace thecoating metal withdrawn from the bath by the strip, and a feed deviceadapted each time it is operated to feed a single pig to said pig supplymeans for delivery to said bath, a system for controlling the operationof said feed device to maintain the surface level of said bath above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, an electrical relay controlling the operation of saidactuating mechanism and including an energizing circuit effective whenclosed to render said actuating mechanism operative and when opened torender said actuating mechanism inoperative, a normally closed limitswitch in said circuit, a control switch for closing said circuit, meansresponsive to the level of metal in said bath falling below saidpredetermined minimum for operating said control switch to close saidcircuit, and means responsive to the completion of a pig feedingoperation by said feed device for momentarily actuating said limitswitch to open position to open said circuit.

14. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto,means for supplying pigs of coating metal to said bath to replace thecoating metal withdrawn from the bath by the strip, and a feed deviceadapted each time it is operated to feed a single pig to said pig supplymeans for delivery to said bath, a system for controlling the operationof said feed device to maintain the surface. level of said bath above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, an electrical relay controlling the operation of saidactuating mechanism and including an energizing circuit effective whenclosed to render said actuating mechanism operative and when opened torender said actuating mechanism inoperative, a normally closed limitswitch in said circuit, a control switch in said circuit movable betweenopen and closed positions, means for operating said control switchbetween its open and closed positions and for maintaining it in its openposition for a predetermined interval of time after each movement toclosed position, means responsive to the level of metal in said bathfalling below said predetermined minimum for operating said controlswitch operating means, and means responsive to the completion of a pigfeeding operation by said feed device for momentarily actuating saidlimit switch to open position to open said circuit.

.15. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto,means for supplying pigs of coating metal to said bath to replace thecoating metal withdrawn from the bath by the strip, and a feed de viceadapted each time it is operated to feed a single pig to said pig supplymeans for delivery to said bath, a system for controlling the operationof said feed device to maintain the surface level of said bath above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, a control relay for rendering said actuating mechanismoperative, a control circuit for energizing said control relay andhaving a normally open first relay switch therein, an operating relay,an operating circuit for energizing said operating relay and having amain circuit and a pair of branch energizing circuits connectedtherewith, a normally closed limit switch in said main circuit, one ofsaid branch energizing circuits having a normally open second relayswitch therein and the other having a control switch therein, meansresponsive to the level of metal in said bath falling below saidpredetermined minimum for operating said control switch to energize saidoperating circuit and said operating relay, said operating relay havingconnections for closing both said first and second relay switches uponenergization thereof, and means responsive to the completion of a pigdelivery operation of said feed device by said actuating mechanism formomentarily operating said limit switch to open position to open saidoperating circuit and de-energize said operating relay to therebydeenergize said control circuit and control relay.

16. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto,means for supplying pigs of coating metal to said bath to replace thecoating metal withdrawn from the bath by the strip, and a feed deviceadapted each time it is operated to feed a single pig to said pig supplymeans for delivery to said bath, a system for controlling the operationof said feed device to main- 1 1 tain the surface level of said bathabove a predetermined minimum comprising actuating means for operatingsaid feed device, means for producing a fluid pressure varying with thelevel of metal in said bath, and means responsive to said fiuid pressurefalling to a predetermined minimum value for operating said actuatingmeans.

17. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto,means for supplying pigs of coating metal to said bath to replace thecoating metal withdrawn from the bath by the strip, and a feed deviceadapted each time it is operated to feed a single pig to said pig supplymeans for delivery to said bath, a system for controlling the operationof said feed device to maintain the surface level of said bath above apredetermined minimum comprising actuating means for operating said feeddevice, means controlling the operation of said actuating means, andmeans responsive to the level of metal in said bath falling below saidpredetermined minimum for rendering said control means operative, saidcontrol means including means for eflecting intermittent operations ofsaid actuating means and for introducing a timed interval between eachoperation of said feed device thereby sufiicient for said levelresponsive means to respond to the change in level of metal in said bathcaused by the pig added by each operation of said feed device.

18. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto,means for supplying pigs of coating metal to said bath to replace thecoating metal withdrawn from the bath by the strip, and a feed deviceadapted each time it is operated to feed a single pig to said pig supplymeans for delivery to said bath, a system for controlling the operationof said feed device to maintain the surface level of said bath above apredetermined minimum comprising an actuating mechanism for operatingsaid feed device, a relay controlling the operation of said actuatingmechanism, means responsive to the level of metal in said bath fallingbelow said predetermined minimum for operating said relay to render saidactuating mechanism operative, and means responsive to the completion ofa pig feeding operation of said feed device by said actuating means foroperating said relay to render said actuating mechanism inoperative.

' 19. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto, anda feed mechanism adapted each time it is operated to feed a single solidpig of coating metal. to said bath to replace the coating metalwithdrawn from the bath by the strip, a system for controlling theoperation of said feed mechanism to maintain the surface level of saidbath above a predetermined minimum comprising actuating means foroperating said feed mechanism, means controlling the operation of saidactuating means, and means responsive to the level of metal in said bathfalling below said predetermined minimum for operating said controllingmeans.

20. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of' coating metal thereto, anda feed mechanism adapted each time it is operated tofeed a single solidpig of coating metal to said bath to replace the coating metal withdrawnfrom the bath by the strip, a system for controlling the operation ofsaid feed mechanism to maintain the surface level of said bath above apredetermined minimum comprising actuating means for operating said feedmechanism, means controlling the operation of said actuating means,means responsive to the level of metal in said bath falling below saidpredetermined minimum for operating said controlling means, and meansresponsive to a pig feeding operation of said feed mechanism by saidactuating means for rendering said controlling means temporarilyinoperative.

21. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto, anda feed mechanism adapted each time it is operated to feed a single solidpig of coating metal to said bath to replace the coating metal withdrawnfrom the bath by the strip, a system for controlling the operation ofsaid feed mechanism to maintain the surface level of said bath above apredetermined minimum comprising actuating means for operating said feedmechanism, a tube extending into said bath and having an outletpositioned below the surface level of the coating metal therein, meansfor forcing a gas at a constant rate through said outlet whereby thepressure of the gas in said tube at a point remote from said outletvaries with the surface level of said bath, and means responsive to saidpressure falling to a predetermined minimum for operating said actuatingmeans.

22. In metal coating apparatus having a bath of coating metal throughwhich strip is passed to apply a covering of coating metal thereto, anda feed mechanism adapted each time it is operated to feed a single solidpig of coating metal to said bath to replace the coating metal withdrawnfrom the bath by the strip, a system for controlling the operation ofsaid feed mechanism to maintain the surface level of said bath above apredetermined minimum comprising actuating means for operating said feedmechanism, a tube extending into said bath and having an outlet positionbelow the surface level of the coating metal therein, means for forcinga gas at a constant rate through said outlet whereby the pressure of thegas in said tube at a point remote from said outlet varies with thesurface level of said bath, and means responsive to said pressurefalling to a predetermined minimum for operating said actuating means,said pressure responsive means including means for effectingintermittent operations of said actuating means and for introducing apredetermined time interval between each operation thereby of said feedmechanism.

References Cited in the file of this patent UNITED STATES PATENTS2,333,543 Martin Nov. 2, 1943 2,415,644 Leonhard et al Feb. 11, 19472,670,708 Kalberkamp Mar. 2, 1954 UNITED STATES PATENT OFFICECERTIFICATE ()F CORRECTION Patent No, 2,841,111 July 1, 1958 Preston L,Walker 11 It is herebi certified that error appears in the-printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 5 line 61, for "established" read -.-establishes=- column 8, line37,. strike outlsaid", second occurrence; line 60, before "switch"insert -limit-==.

Signed and sealed this 7th day of October 1958.

Commissioner of Patents Attesting Officer

